The hard reality of the world is that adults prey on children. If my kid was a loner, I'd probably be doubly vigilant about adults showing interest. I'd want to know who the person is , how my kid knows them, what is the stated reason for wanting to spend time together, etc. If there's no clear purpose to the relationship, (mentor/coach/teacher), I'd discourage it, but more likely, not allow it all all, especially if it is a man, and unknown to me.